1. Technical Field of the Invention
The present invention relates to baker""s yeast having both freezing tolerance and drying tolerance, and more precisely, to novel dry yeast including instant dry yeast capable of being used in baking bread from frozen dough.
Though being dry, the novel yeast of the invention has excellent freezing tolerance. Frozen dough as produced through the process of preparing dough with the yeast of the invention followed by incubating and freezing it is tolerant to long-term frozen storage of 2 weeks or longer, from which is produced good bread.
Therefore, the invention greatly contributes to developments in the baking industry, especially in the frozen dough industry.
2. Prior Art
The process of baking bread from frozen dough has heretofore been developed for the purpose of saving time and labor in bakeries and for the purpose of always providing fresh bread for consumers, and is now the mainstream process in the current baking industry.
The problem with the baking process from frozen dough is that the activity of the yeast used is greatly lowered while the dough having been incubated by the action of the yeast is frozen and stored for a certain period of time, then thawed and fermented. In order to solve the problem, in general, exclusively used are freezing-tolerant yeast products in the frozen dough-baking process.
On the other hand, dry yeast as prepared by drying raw yeast has heretofore been used for the purpose of ensuring its preservability and storage stability, and is being improved. Recently, instant dry yeast (active dry yeast) products have been developed, some of which have been put into practical use.
In fact, instant dry yeast has brought about drastic improvements in baking operations over pressed raw yeast, and the storage stability of the yeast itself has been improved greatly. However, in the process of producing dry yeast, in general, if strains having drying tolerance or those having been so mutated through specific cultivation that they are tolerant to drying are not used, the activity of the yeast produced is greatly lowered after it is dried. Even if raw yeast is cultivated under specific conditions for the purpose of making it tolerant to drying to thereby obtain dry yeast, it is difficult to produce dry yeast products still having the favorable properties intrinsic to the yeast, including the fermenting ability of the yeast. The properties of dough comprising the dry yeast as prepared in that manner, and also the taste of bread from the dough will be poor. Anyhow, dry yeast could not be substituted for raw yeast in some baking conditions, because of its properties including the temperature sensitivity and the influence on the physical properties of dough.
Given that situation, at present, the application of instant dry yeast is for only specific baking processes for limited types of bread such as French bread and the like. In particular, the fermenting power of dry yeast having been kept at low temperatures, for example, in frozen dough is greatly lowered when the frozen dough that contains the yeast is thawed and fermented, like that of raw yeast products in frozen dough, and, in general, it is known that the degree of reduction in the fermenting power of dry yeast in frozen dough is greater when the pre-fermenting the dough prior to being frozen is longer and when the time for storing the frozen dough is longer. In addition, it is also known that, when contacted with water, dry yeast releases intracellular reducing substances such as glutathione and others to a much greater degree than raw yeast, thereby having some negative influences to no small extent on the physical properties of dough containing it.
In order to obviate this problem, there is an attempt to suppress the reduction in activity due to contact with low-temperature water and hydration, in which a re-hydrating agent for instant dry yeast is used in producing instant dry yeast, which is selected from specific fatty acid esters and their combinations, along with a novel activity-protecting agent that may be selected from locust bean gum, cutch gum, yeast extract, sodium carboxymethyl cellulose (CMC) and the like (see U.S. Pat. No. 4,764,472). Also employed in some cases is an antioxidant such as ascorbic acid or the like, as a stabilizer, in an amount of about 0.3% relative to the yeast product (see Japanese Patent Application Laid-Open Hei-7-39370).
However, the recent tendency in the art is toward the minimization of such additives in dough, for which freezing-tolerant instant dry yeast is desired.
In consideration of the current technical level in the art noted above, the present invention has been made for the purpose of newly developing novel baker""s yeast having both freezing tolerance and drying tolerance.